Dos and Don'ts of Conditional Compile [closed]

Question

When is doing conditional compilation a good idea and when is it a horribly bad idea?

By conditional compile I mean using #ifdefs to only compile certain bits of code in certain conditions. The #defineds themselves may be in either a common header file or introduced via the -D compiler directive.

Answer 1

The good ideas:

• header guards (you can't do much better for portability)
• conditional implementation (juggling with platform differences)
• debug specific checks (asserts, etc...)
• per suggestion: extern "C" { and } so that the same headers may be used by the C++ implementation and by the C clients of the API

The bad idea:

• changing the API between compile flags, since it forces the client to changes its uses with the same compile flags... urk!